1. Field of the Invention
The present invention relates to a projector-type vehicle headlight.
2. Description of the Related Art
A conventional projector-type vehicle headlight is disclosed in Utility Model Laid-Open No. H06-50106. The conventional (vehicle headlight includes a light source (such as a bulb), a reflector (such as a concave mirror), a projector lens (such as a convex lens), and a shade. Light emitted from the light source is reflected to the projector lens by the reflector. The projector lens projects the reflected light in front of a vehicle. The shade has the shape along a meridional image surface that is generated by the projected light from the projector lens. The shade creates a certain light distribution pattern including a cut-off line (a cut line) that blocks a portion of the reflected light from the reflector to the projector lens. An operational mechanism of the conventional vehicle headlight is described below. When the light source lights up, light emitted from the light source is reflected to the shade and the projector lens by the reflector. The shade blocks a portion of the reflected light. The rest of the reflected light, which is not blocked by the shade, is projected forward the vehicle in the certain light distribution pattern including the cut-off line by the projector lens.
It is desirable that a vehicle headlight has lower production costs. One approach is to make the shade from a thin steel sheet instead of aluminum die-casting alloy. However, if the thin steel sheet is simply flat, a linear edge of the shade does not match with a curve of the meridional image surface of the projector lens. On the other hand, if the edge of the shade is overlapped with the meridional image surface at those center portions, gaps occur between the edge and the meridional image surface at both sides that leads to occurrence of blurs at the both sides of the cut-off line of the light distribution pattern. Moreover, amounts of light are not even by positions of the light distribution pattern. Namely, amounts of light at the both sides of the cut-off line are smaller than that for the center portion. Therefore, it may happen that enough amounts of light cannot be obtained at the both sides of the cut-off line. FIG. 9 depicts iso-illuminance curves (iso-intensity curves) that are obtained by using vehicle headlights according to the conventional technique and an embodiment of the present invention. A dashed-two dotted line represents an iso-illuminance curve for the conventional vehicle headlight. A solid line (the outermost solid line) represents an iso-illuminance curve for the vehicle headlight according to the embodiment of the present invention. It can be seen that, the iso-illuminance curve indicated by the dashed-two dotted line is narrower than the same for indicated by the outermost solid line.
A reason why the edge of the shade is overlapped with the meridional image surface at those center portions is described below. If the edge is overlapped with the meridional image surface at those both sides, a gap occurs between the edge and the meridional image surface at the center portions that leads to occurrence of a blur at the center portion of the cut-off line. Therefore, the shape of the cut-off line at the center portion becomes unclear. Moreover, an amount of light at the center portion of the cut-off line in the light distribution pattern becomes larger than the same for on the both sides that disadvantageously leads to generation of glare at the center portion of the cut-off line. In consideration of these facts, it is common in vehicle headlamps to overlap the edge with the meridional image surface at those center portions.
One approach to overcome the shortage of the amounts of light at both the sides of the cut-off line could be to bent downward both ends of the edge, thereby increasing the amounts of light around the both sides of the cut-off line. However, in this approach, both the ends of the cut-off line are lifted upward, which can lead to generation of glare at the both ends of the cut-off line. Especially, in the vehicle headlight being compatible with the adaptive front-lighting system (AFS) that has been adopted in recent years, the possibility of generation of glare increases remarkably because a lighting direction in the light distribution pattern rotates from side to side as a lamp unit rotates around a vertical axis (for example, a vertical axis V-V shown in FIGS. 2 and 11) when the vehicle is turning.
One approach is to make the shade, which is made of thin steel sheets, curved along the meridional image surface. However, production costs of such a shade increases, because the production design becomes complicated to have the curve along the meridional image surface.